The SND format is a variant of the AU sound format, so it should be playable in any application that supports them (WinAMP, foobar2000, WMP, etc). But I'm guessing it's not, seeing as you haven't had any luck playing them, and that these DC SND files are actually an entirely different (proprietary... ugh, hate that word
) format.
One thing to do is to try importing the sound as raw data into an app like
Audacity and keep fiddling with the different settings (byte order, frequency, sampling rate etc) when you import the file until you get something that sounds decent. But if it's a compressed format, you probably won't be able to get anything that sounds much good, in which case I suppose you'd have to wait for an SND to WAV converter to be developed, or for what spunky suggested.
Also, have a look inside the file with a hex editor and post here the first 5-10 or so lines of data in the file, might be able to identify what it is that way (this is how I IDed some mysterious AIFC audio files once from the 3DO version of Cannon Fodder, and I did actually find a converter for them in the end, albeit only the source code, which I haven't been able to compile).
